The pill

I’ve heard during pregnancy, while using a contraceptive, you will miss a period and others say they got their period so they had no idea. My first pregnancy I wasn’t on birth control and I missed my period. Now on bc, I usually bleed for 5-7 days. I stopped 🩸 on day 3. This just seems odd to me. I’ve never had such a short period. Should I be concerned? Any insights or advice would be much appreciated